Pump for conveying an exhaust gas aftertreatment medium particularly a urea-water solution, for diesel engines

ABSTRACT

A pump for conveying an exhaust gas treatment medium in diesel engines has a pump housing and a piston arranged in the pump housing and movable in the pump housing against a counterforce. The piston pumps an exhaust gas treatment medium form at least one inlet of the pump to at least one outlet of the pump. A diaphragm separates the piston from the exhaust gas treatment medium. The counterforce is provided by at least one spring that is a pressure spring.

The invention relates to a pump for conveying an exhaust gas after treatment medium, in particular, a urea/water solution, for diesel engines according to the preamble of claim 1.

Cleaning devices for diesel vehicles are known in which the exhaust gas of diesel engines is treated with a medium, preferably a 32.5% urea/water solution, in order to reduce or remove completely the nitrous oxides in the exhaust gas. For conveying the medium, a pump is provided that pumps the medium from a reservoir.

The invention has the object to configure the pump of the aforementioned kind such that by means of the pump the exhaust gas after treatment medium can be properly and reliably conveyed under the conditions occurring within diesel vehicles.

This object is solved for the pump of the aforementioned kind in accordance with the present invention with the characterizing features of claim 1.

In the pump according to the invention, the pump element is a piston that is movable against a counterforce during the pumping operation. The piston is separated by a diaphragm from the medium to be pumped. By means of the pump according to the invention sufficiently high pressures can be achieved. Since the piston is separated from the medium by a diaphragm, it is corrosion-resistant because it does not come into contact with the medium. The diaphragm seals the piston so that a shaft seal is not required in the area in contact with the medium. The pump is characterized by a simple configuration and a long service life.

Further features of the invention result from the dependent claims, the description, and the drawing.

The invention will be explained in more detail with the aid of two embodiments illustrated in the drawings. It is shown in:

FIGS. 1 and 2 in axial section a pump according to the invention in a first and a second pump position, respectively;

FIG. 3 a second embodiment of the pump according to the invention in a representation corresponding to that of FIG. 2;

FIG. 4 the detail Z of FIG. 3 in an enlarged illustration.

The pump is advantageously suitable for use in exhaust gas after treatment devices for diesel engines. Of course, it can also be used for other pumping purposes.

The pump has a housing 1 that is provided at one end face with a cylindrical projection 2. At least one solenoid 3 is embedded in the housing 1. The housing 1 has a central axial receiving chamber 4 having at its inner wall a sleeve-shaped slide bearing 5. The bearing is positioned with the first end on a radially inwardly oriented annular shoulder 6 that projects away from the inner wall 7 of the receiving chamber 4.

A cup-shaped piston 8 is arranged in the slide bearing 5 so as to be axially movable against the force of at least one pressure spring 9. One end of the pressure spring 9 is supported on the bottom 10 of the piston and the other end on the bottom side of an adjusting screw 11 that is screwed into the projection 2. By means of the adjusting screw 11, the pretension of the pressure spring 9 can be adjusted continuously. For centering the pressure spring 9, the adjusting screw 11 is provided at its underside with a central projection 12 that projects into the appropriate end of the pressure spring 9.

The piston 8 is provided at the end facing the adjusting screw 11 with a radially outwardly oriented flange 13 that rests against the radially outwardly oriented shoulder 14 of the inner wall 7 of the receiving chamber 4 in a first position (FIG. 2) of the piston 8. The adjusting screw 11 has at its circumference an annular wall 15 having an inner wall for guiding the flange 13 of the piston 8.

A pump head 16 is connected, preferably by screwing, to the end face of the housing 1 that is remote from the adjusting screw 11. The pump head 16 has a housing 17 with a radially outwardly oriented flange 18 with which the pump head 16 rests areally and sealingly against the end face of the housing 1. Along the rim of the flange 18 fastening screws 19 are provided with which the pump head 16 is screwed onto the housing 1. The head of the fastening screws 19 is positioned advantageously recessed within the flange 18.

In the pump head there are two check valves 20, 21 that are arranged at a spacing from one another; each is arranged in a receiving chamber 22, 23 of the pump head 16. In the receiving chamber 22 there is a valve body 24 having an outer diameter that is smaller than the outer diameter of the receiving chamber 22. The valve body 24 is loaded by at least one pressure spring 25 in the direction toward its closed position illustrated in FIG. 1 in which it closes off a bore 26 in the pump head 16. The axis-parallel bore 26 connects the receiving chamber 22 to a pump chamber 27 that is closed off by a diaphragm 28. The pump chamber 27 is formed essentially by a recess of the end face of the pump head 16. The diaphragm 28 has a reinforced circumferentially extending rim 29 that is clamped between the housing 1 and the flange 18 of the pump head 16. The diaphragm 28 has at its side facing the piston 8 a central projection 30 that penetrates a central bore 31 of the bottom 10 of the piston 8. The free end of the projection 30 has a wider portion 32 that serves as an axial securing means of the diaphragm 28 relative to the piston 8. The wider portion 32 rests at the inner side of the piston bottom 10 and is designed such that the diaphragm 28 is connected captively to the piston 8.

On the side of the pump head 16 opposite the bore 26, a bore 33 opens into the receiving chamber 22; the bore is provided in the connecting plate 34. The plate is fastened to the end face of the pump head 16 that is facing away from the housing 1.

In the receiving chamber 23 of the pump head 16 there is also a valve body 35 that is identical to the valve body 24 but is arranged in the receiving chamber 23 in a 180° rotated position relative to the valve body 24. The valve body 35 closes a bore 36 that extends parallel to the bore 33 in the connecting plate 34. The valve body 35 is loaded by at least one pressure spring 37 in the receiving chamber 23 in the direction toward its closed position (FIG. 2). The outer diameter of the valve body 35 is smaller than the diameter of the receiving chamber 23. A bore 38 is provided in the pump head 16 parallel to the bore 26 and opens into the receiving chamber 23. The bore 38 connects the pump chamber 27 to the receiving chamber 23.

The pressure spring 25 of the check valve 20 is supported with one end on the connecting plate 34 and with its other end on the valve body 24. The pressure spring 37 is supported with one end on the bottom of the receiving chamber 23 and with its other end on the valve body 35.

The bores 33, 36 open into connectors 39, 40 that are provided at the end face of the connecting plate 34 facing away from the pump head 16 and through which the medium to be conveyed is sucked in or discharged.

In the position according to FIG. 1, current is supplied to the solenoid 3 so that the piston 8 is moved against the force of the pressure spring 9 until the piston with its flange 13 rests against the adjusting screw 11 (FIG. 1). The diaphragm 28, because it is axially fixedly connected to the piston 8, is entrained so that vacuum is generated in the bores 26, 38. This has the result that the valve body 24, assisted by the force of the pressure spring 25, moves into the closed position in which it closes the bore 26. The valve body 35 is lifted off the connecting plate 34 by the generated vacuum acting against the force of the pressure spring 37. In this way, through the connector 40 and the bore 36 the medium can reach the receiving chamber 23. Here, the sucked-in medium flows past the valve body 35 through the bore 38 into the pump chamber 27.

Subsequently, the current supply to the solenoid 3 is switched off. This has the result that the piston 8 is returned by the force of the pressure spring 9 so far that its flange 13 contacts the shoulder 14 of the pump housing 1 (FIG. 2). This axial displacement process causes the diaphragm 28 to be entrained and elastically deformed. The medium contained in the pump chamber 27 is pressurized. This has the result that the medium moves the valve body 35 into the closed position illustrated in FIG. 2, assisted by the force of the pressure spring 37. In this way, the bore 36 in the connecting plate 34 is blocked. At the same time, however, the valve body 24 is pushed back by the pressurized medium against the force of the pressure spring 25 so that the bore 26 in the pump head 16 is released. The medium reaches the receiving chamber 22 and can flow past the valve body 24 into the bore 33 and thus into the connector 39.

The level of the pump pressure is dependent on the spring force of the pressure spring 9 with which the piston 8 is actuated. By means of the adjusting screw 11 the pump pressure can be fine-adjusted after mounting.

Advantageously, the end face 41 of the piston bottom 10 facing the diaphragm 28 is curved (FIG. 1) such that the diaphragm 28 can rest in the deflected position according to FIG. 2 areally against the end face 41 (FIG. 2). In this way, the diaphragm 28 is optimally supported and therefore wears only minimally.

The pump is the combination of an oscillating piston pump and a diaphragm pump. The oscillating piston part with the piston 8 serves as a maintenance-free drive while the diaphragm 28 provides the pumping member. During the pumping action, only the diaphragm 28 is in contact with the medium but not the piston 8. Accordingly, the material of the diaphragm 28 can be matched optimally to the medium to be pumped. The piston 8 does not come into contact with this medium and can therefore be manufactured of materials that are accordingly less expensive.

The pump can generate pressures, for example, within the range of approximately 5 bar. The pump is corrosion-resistant relative to aqueous solutions because the oscillating piston part is sealed by the diaphragm 28 relative to the medium. In the diaphragm pump part a shaft seal is not provided so that problems related with such seals do not occur. The described pump is freeze-protected because the pump piston 8 in the rest state (solenoid not supplied with current, FIG. 2) is in the position of smallest dead pumping volume 27. When the medium freezes, the resulting additional volume can be taken up by the piston 8 that retreats against the spring 9. The pump can be easily heated by means of the solenoid 3 so that a self-contained thawing of the medium after a possible freezing action is enabled. possible. The pump operates maintenance-free at least over the service life of the vehicle in which it is mounted.

The pump according to FIGS. 3 and 4 differs from the afore described embodiment essentially in that instead of the piston spring 9 a plate spring 9′ is provided that is integrated into the diaphragm 28 and is tightly enclosed by the diaphragm. The plate spring 9′ is mounted on a fastening part 42 which is also embedded in the diaphragm 28 and from which the projection 30 projects that projects out of the diaphragm 28 and is configured as a threaded pin. It is screwed into the bottom 10 of the piston 8. The fastening part 42 and the projection 30 together form advantageously a unitary part. The diaphragm 28 is comprised preferably of thermoplastic elastomer or vulcanized elastomer.

FIG. 3 shows the piston 8 in a position in accordance with FIG. 2 of the preceding embodiment. The solenoid 3 is not supplied with current and the piston 8 is moved by the force of the plate spring 9′ into a position such that it rests with its flange 13 against the shoulder 14 of the pump housing 1. The diaphragm 28 rests areally on the curved end face 41 of the piston bottom 10.

When the coil 3 is supplied with current, the piston 8 is moved against the force of the plate spring 9′ until it comes to rest with its flange 13 against the adjusting screw 11.

In other respects, the function of the pump is identical to that of the embodiment of FIGS. 1 and 2. 

1.-27. (canceled)
 28. A pump for conveying an exhaust gas treatment medium in diesel engines, the pump comprising: a pump housing; a piston arranged in the pump housing and movable in the pump housing against a counterforce, wherein the piston pumps an exhaust gas treatment medium from at least one inlet of the pump to at least one outlet of the pump; and a diaphragm separating the piston from the exhaust gas treatment medium.
 29. The pump according to claim 28, wherein the piston is a hollow piston.
 30. The pump according to claim 28, comprising at least one spring generating the counterforce.
 31. The pump according to claim 30, wherein the at least one spring is a pressure spring.
 32. The pump according to claim 30, wherein the at least one spring is a plate spring.
 33. The pump according to claim 32, wherein the plate spring is integrated into the diaphragm.
 34. The pump according to claim 33, wherein the plate spring is tightly enclosed by the diaphragm.
 35. The pump according to claim 28, wherein the diaphragm is comprised of thermoplastic elastomer or vulcanized elastomer.
 36. The pump according to claim 28, comprising at least one solenoid surrounding the piston.
 37. The pump according to claim 36, wherein the piston is movable by applying current to the at least one solenoid.
 38. The pump according to claim 28, wherein the piston has a bottom.
 39. The pump according to claim 38, wherein the diaphragm is fixedly connected to the piston in a movement direction of the piston.
 40. The pump according to claim 39, wherein the diaphragm is connected to the bottom of the piston.
 41. The pump according to claim 38, wherein the diaphragm has a projection that projects through the bottom of the piston.
 42. The pump according to claim 41, further comprising a fastening part embedded in the diaphragm, wherein the projection projects from the fasting part.
 43. The pump according to claim 42, comprising a plate spring generating the counterforce, wherein the plate spring is integrated into the diaphragm and is secured on the fasting part
 44. The pump according to claim 41, wherein the projection is a threaded pin.
 45. The pump according to claim 44, wherein the threaded pin is screwed into the bottom of the piston.
 46. The pump according to claim 28, comprising at least one solenoid surrounding the piston, wherein the piston is movable by applying current to the at least one solenoid, wherein the diaphragm rests areally against the bottom of the piston when the solenoid is not actuated.
 47. The pump according to claim 28, wherein the diaphragm has a rim that is clamped between the pump housing and a pump head of the pump.
 48. The pump according to claim 47, wherein the diaphragm delimits a pump chamber.
 49. The pump according to claim 48, wherein the pump chamber is provided in the pump head.
 50. The pump according to claim 49, comprising a first check valve that is adapted to close a supply path to the pump chamber.
 51. The pump according to claim 50, comprising a second check valve that is adapted to close the at least one outlet.
 52. The pump according to claim 51, wherein the first and second check valves operate in opposite directions relative to one another.
 53. The pump according to claim 51, wherein the pump head has first and second receiving chambers, wherein first check valve has a first valve body arranged in the first receiving chamber and the second check valve has a second valve body arranged in the second receiving chamber.
 54. The pump according to claim 53, wherein an outer diameter of the first and second valve bodies is smaller than an inner diameter of the first and second receiving chambers, respectively.
 55. The pump according to claim 53, wherein the first and second receiving chambers are connected to the pump chamber. 